The present invention relates to a magnetic disk memory device, and more particularly to a magnetic disk memory device having an improved housing.
Generally, the components or constituent elements of a magnetic disk memory device include a spindle motor which supports and rotates a magnetic disk for recording information, a positioning mechanism which supports a magnetic head for reading and writing information from and to the magnetic disk and causes the movement of the magnetic head on the magnetic disk so that the head moves to any position on the disk in cooperation with the rotation of the disk. These components are incorporated in a housing. In such a magnetic disk memory device, the recording and reproduction are made in a state in which the magnetic head takes a very low floating condition. Therefore, even a small amount of dust should be prevented from entering into the housing. Accordingly, the housing is placed in a substantially closed condition. Also, there is generally known a magnetic disk memory device having a structure in which a printed wiring board including a control circuit for causing a magnetic head to perform the writing into a magnetic disk and the reading from the magnetic disk and a circuit for controlling the operation of a spindle motor and a motor included in a head positioning mechanism are mounted on the outer side of a housing.
In recent years, a reduction in thickness or size was required for such magnetic disk memories. The size shows a yearly decrease. The conventional approach to the reduction in thickness is made by improving constituent elements included in a housing.
JP-A-3-189957 has disclosed a spindle motor the height of which is made smaller than that of the conventional spindle motor. The disclosed spindle motor is constructed such that only one end of a spindle is fixed to a housing and a hub is attached to the spindle through a bearing so that a motor coil and a magnet are incorporated in the hub and a printed wiring board for the spindle motor is brought into the hub. Also, JP-A-3-189958 has disclosed a magnetic disk memory device in which a member including a hub and a spindle incorporated in one is used in order to make the height of a spindle motor smaller than that of the conventional spindle motor. In the disclosed magnetic disk memory device, the influence of the spindle motor given on the height of a housing is diminished in such a manner that the housing for holding the spindle through a bearing is fixed in a hole provided in a base portion of the magnetic disk memory device. In these prior arts, the reduction in device thickness is attained by making the improvement in which the height of a constituent element included in a housing is reduced.
As a further technique for reduction in thickness of a magnetic disk memory device, JP-A-4-79092 has disclosed a technique in which the inner wall surface of a housing of a so-called FDD (floppy disk drive) having a flexible magnetic disk as a recording or storage medium is processed in order to acquire the substantial height of the interior of the housing. In this prior art, the housing is composed of a base portion and a cover portion and a recess is formed on the inner wall of the cover portion by press working.
JP-A-3-286488 has disclosed a technique concerning the connection of a spindle motor which is included in a closed housing and a printed wiring board which is arranged outside of the housing and on which a circuit for controlling the spindle motor is placed. The thickness of the whole of a device is substantially determined by the thickness of the housing and a distance between the housing and the printed wiring board provided outside of the housing. In the disclosed technique, the distance between the printed wiring board and the housing is reduced in such a manner that a connector for electrically connecting the spindle motor and the control circuit on the printed wiring board is provided in the wall of the housing.
However, since the reduction in size of mechanism elements such as a spindle motor and the reduction in thickness of a printed wiring board have a direct relation with the performance, a further reduction in size and thickness is considerably difficult. Also, the reduction in thickness of a housing has a limit since the housing is formed by a casting such as a die-cast. Regarding the structure of the housing, even if only a part of the specification is changed, that is, even if electronic parts on the printed wiring board are changed, a strength required for the housing must be newly considered or the housing must be fabricated again. Therefore, the realization of reduction in housing thickness has a very poor efficiency.
Accordingly, the formation of the recess in the inner wall surface of the housing contributes to no considerable acquisition of the height of the interior of the housing and has a very low degree of freedom for a change in design specification. Also, even with the construction in which the connecting portion of the connector is provided in the inner wall surface of the housing, the degree of freedom for the change in design specification is very small.